The Hypertext Transfer Protocol (HTTP) is an application-level protocol for distributed, collaborative, hypermedia information systems. HTTP has been in use by the World Wide Web global information initiative since 1990. This document is Part 7 of the seven-part specification that defines the protocol referred to as "HTTP/1.1" and, taken together, obsoletes RFC 2616. Part 7 defines HTTP Authentication.
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The changes in this draft are summarized in Appendix B.13.
This document defines HTTP/1.1 access control and authentication. It includes the relevant parts of RFC 2616 with only minor changes, plus the general framework for HTTP authentication, as previously defined in "HTTP Authentication: Basic and Digest Access Authentication" ([RFC2617]).¶
HTTP provides several OPTIONAL challenge-response authentication mechanisms which can be used by a server to challenge a client request and by a client to provide authentication information. The "basic" and "digest" authentication schemes continue to be specified in RFC 2617.¶
An implementation is not compliant if it fails to satisfy one or more of the "MUST" or "REQUIRED" level requirements for the protocols it implements. An implementation that satisfies all the "MUST" or "REQUIRED" level and all the "SHOULD" level requirements for its protocols is said to be "unconditionally compliant"; one that satisfies all the "MUST" level requirements but not all the "SHOULD" level requirements for its protocols is said to be "conditionally compliant".¶
This specification uses the ABNF syntax defined in Section 1.2 of [Part1] (which extends the syntax defined in [RFC5234] with a list rule). Appendix A shows the collected ABNF, with the list rule expanded.¶
The following core rules are included by reference, as defined in [RFC5234], Appendix B.1: ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls), DIGIT (decimal 0-9), DQUOTE (double quote), HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed), OCTET (any 8-bit sequence of data), SP (space), VCHAR (any visible USASCII character), and WSP (whitespace).¶
HTTP provides a simple challenge-response authentication mechanism that can be used by a server to challenge a client request and by a client to provide authentication information. It uses an extensible, case-insensitive token to identify the authentication scheme, followed by a comma-separated list of attribute-value pairs which carry the parameters necessary for achieving authentication via that scheme.¶
auth-scheme = token auth-param = token "=" ( token / quoted-string )
The 401 (Unauthorized) response message is used by an origin server to challenge the authorization of a user agent. This response MUST include a WWW-Authenticate header field containing at least one challenge applicable to the requested resource. The 407 (Proxy Authentication Required) response message is used by a proxy to challenge the authorization of a client and MUST include a Proxy-Authenticate header field containing at least one challenge applicable to the proxy for the requested resource.¶
The authentication parameter realm is defined for all authentication schemes:¶
realm = "realm" "=" realm-value realm-value = quoted-string
The realm directive (case-insensitive) is required for all authentication schemes that issue a challenge. The realm value (case-sensitive), in combination with the canonical root URI (the scheme and authority components of the effective request URI; see Section 4.3 of [Part1]) of the server being accessed, defines the protection space. These realms allow the protected resources on a server to be partitioned into a set of protection spaces, each with its own authentication scheme and/or authorization database. The realm value is a string, generally assigned by the origin server, which can have additional semantics specific to the authentication scheme. Note that there can be multiple challenges with the same auth-scheme but different realms.¶
A user agent that wishes to authenticate itself with an origin server -- usually, but not necessarily, after receiving a 401 (Unauthorized) -- MAY do so by including an Authorization header field with the request. A client that wishes to authenticate itself with a proxy -- usually, but not necessarily, after receiving a 407 (Proxy Authentication Required) -- MAY do so by including a Proxy-Authorization header field with the request. Both the Authorization field value and the Proxy-Authorization field value consist of credentials containing the authentication information of the client for the realm of the resource being requested. The user agent MUST choose to use one of the challenges with the strongest auth-scheme it understands and request credentials from the user based upon that challenge.¶
The protection space determines the domain over which credentials can be automatically applied. If a prior request has been authorized, the same credentials MAY be reused for all other requests within that protection space for a period of time determined by the authentication scheme, parameters, and/or user preference. Unless otherwise defined by the authentication scheme, a single protection space cannot extend outside the scope of its server.¶
If the origin server does not wish to accept the credentials sent with a request, it SHOULD return a 401 (Unauthorized) response. The response MUST include a WWW-Authenticate header field containing at least one (possibly new) challenge applicable to the requested resource. If a proxy does not accept the credentials sent with a request, it SHOULD return a 407 (Proxy Authentication Required). The response MUST include a Proxy-Authenticate header field containing a (possibly new) challenge applicable to the proxy for the requested resource.¶
The HTTP protocol does not restrict applications to this simple challenge-response mechanism for access authentication. Additional mechanisms MAY be used, such as encryption at the transport level or via message encapsulation, and with additional header fields specifying authentication information. However, these additional mechanisms are not defined by this specification.¶
Proxies MUST be completely transparent regarding user agent authentication by origin servers. That is, they MUST forward the WWW-Authenticate and Authorization headers untouched, and follow the rules found in Section 4.1. Both the Proxy-Authenticate and the Proxy-Authorization header fields are hop-by-hop headers (see Section 126.96.36.199 of [Part1]).¶
The HTTP Authentication Scheme Registry defines the name space for the authentication schemes in challenges and credentials.¶
Registrations MUST include the following fields: ¶
The request requires user authentication. The response MUST include a WWW-Authenticate header field (Section 4.4) containing a challenge applicable to the target resource. The client MAY repeat the request with a suitable Authorization header field (Section 4.1). If the request already included Authorization credentials, then the 401 response indicates that authorization has been refused for those credentials. If the 401 response contains the same challenge as the prior response, and the user agent has already attempted authentication at least once, then the user SHOULD be presented the representation that was given in the response, since that representation might include relevant diagnostic information.¶
This code is similar to 401 (Unauthorized), but indicates that the client ought to first authenticate itself with the proxy. The proxy MUST return a Proxy-Authenticate header field (Section 4.2) containing a challenge applicable to the proxy for the target resource. The client MAY repeat the request with a suitable Proxy-Authorization header field (Section 4.3).¶
This section defines the syntax and semantics of HTTP/1.1 header fields related to authentication.¶
The "Proxy-Authenticate" response-header field consists of a challenge that indicates the authentication scheme and parameters applicable to the proxy for this effective request URI (Section 4.3 of [Part1]). It MUST be included as part of a 407 (Proxy Authentication Required) response.¶
Proxy-Authenticate = "Proxy-Authenticate" ":" OWS Proxy-Authenticate-v Proxy-Authenticate-v = 1#challenge
Unlike WWW-Authenticate, the Proxy-Authenticate header field applies only to the current connection and SHOULD NOT be passed on to downstream clients. However, an intermediate proxy might need to obtain its own credentials by requesting them from the downstream client, which in some circumstances will appear as if the proxy is forwarding the Proxy-Authenticate header field.¶
The "WWW-Authenticate" response-header field consists of at least one challenge that indicates the authentication scheme(s) and parameters applicable to the effective request URI (Section 4.3 of [Part1]). It MUST be included in 401 (Unauthorized) response messages.¶
User agents are advised to take special care in parsing the WWW-Authenticate field value as it might contain more than one challenge, or if more than one WWW-Authenticate header field is provided, the contents of a challenge itself can contain a comma-separated list of authentication parameters.¶
The Message Header Field Registry located at <http://www.iana.org/assignments/message-headers/message-header-index.html> shall be updated with the permanent registrations below (see [RFC3864]):¶
|Header Field Name||Protocol||Status||Reference|
The change controller is: "IETF (email@example.com) - Internet Engineering Task Force".¶
This section is meant to inform application developers, information providers, and users of the security limitations in HTTP/1.1 as described by this document. The discussion does not include definitive solutions to the problems revealed, though it does make some suggestions for reducing security risks.¶
Existing HTTP clients and user agents typically retain authentication information indefinitely. HTTP/1.1 does not provide a method for a server to direct clients to discard these cached credentials. This is a significant defect that requires further extensions to HTTP. Circumstances under which credential caching can interfere with the application's security model include but are not limited to: ¶
This is currently under separate study. There are a number of work-arounds to parts of this problem, and we encourage the use of password protection in screen savers, idle time-outs, and other methods which mitigate the security problems inherent in this problem. In particular, user agents which cache credentials are encouraged to provide a readily accessible mechanism for discarding cached credentials under user control.¶
This specification takes over the definition of the HTTP Authentication Framework, previously defined in RFC 2617. We thank to John Franks, Phillip M. Hallam-Baker, Jeffery L. Hostetler, Scott D. Lawrence, Paul J. Leach, Ari Luotonen, and Lawrence C. Stewart for their work on that specification.¶
Authorization = "Authorization:" OWS Authorization-v Authorization-v = credentials OWS = <OWS, defined in [Part1], Section 1.2.2> Proxy-Authenticate = "Proxy-Authenticate:" OWS Proxy-Authenticate-v Proxy-Authenticate-v = *( "," OWS ) challenge *( OWS "," [ OWS challenge ] ) Proxy-Authorization = "Proxy-Authorization:" OWS Proxy-Authorization-v Proxy-Authorization-v = credentials WWW-Authenticate = "WWW-Authenticate:" OWS WWW-Authenticate-v WWW-Authenticate-v = *( "," OWS ) challenge *( OWS "," [ OWS challenge ] ) auth-param = token "=" ( token / quoted-string ) auth-scheme = token challenge = auth-scheme 1*SP *( "," OWS ) auth-param *( OWS "," [ OWS auth-param ] ) credentials = auth-scheme ( token / quoted-string / [ ( "," / auth-param ) *( OWS "," [ OWS auth-param ] ) ] ) quoted-string = <quoted-string, defined in [Part1], Section 1.2.2> realm = "realm=" realm-value realm-value = quoted-string token = <token, defined in [Part1], Section 1.2.2>
; Authorization defined but not used ; Proxy-Authenticate defined but not used ; Proxy-Authorization defined but not used ; WWW-Authenticate defined but not used ; realm defined but not used
No significant changes.¶
Closed issues: ¶